1. Field of the Invention
This invention relates to a control system for a hybrid vehicle which has a plurality of prime movers.
The present invention relates to the subject matter contained in Japanese Patent Application No.2003-72588, filed on Mar. 17, 2003, which is expressly incorporated herein by reference.
2. Related Art
In recent year, there has been proposed a hybrid vehicle on which an engine for outputting a power by burning fuel and an electric motor generator for outputting a power by feeding it with an electric power are mounted, and which is capable of transmitting a power from the engine and the motor generator to wheels. In this kind of hybrid vehicle, the engine and the motor generator is controlled on the basis of various conditions so as to improve the fuel economy and to reduce the noise and the exhaust gas emission.
One example of the hybrid vehicle mounting a plurality of prime movers thereon as described above is disclosed in Japanese Patent Laid-Open No. 2002-225578. The disclosed hybrid vehicle has an engine and a second motor generator as the driving force source. Also, a planetary gear mechanism is arranged on a power transmission route between the engine and the second motor generator and the wheels. This planetary gear mechanism has a sun gear, ring gear, and a carrier supporting a pinion gear which meshes with the sun gear and the ring gear. This carrier and the engine are connected each other, and the ring gear is connected with the wheel and the second motor generator. Moreover, the first motor generator is connected with the sun gear. On the other hand, the speed change mechanism is provided on the power transmission route between the ring gear and the second motor generator. Furthermore, there are provided a shifting mechanism for interchanging the speed change mechanism between a low-state and a high-state, and an actuator for controlling the changing mechanism.
In the hybrid vehicle disclosed in above-mentioned publication, a power of at least one of the engine and the motor generator is transmitted through the planetary gear mechanism to the wheel. In case of transmitting a power of the second motor generator to the wheel, a control to change the speed change mechanism to the low-state or the high-state on the basis of a demand torque is executed. Here, a hybrid vehicle having an engine and a motor generator as a prime mover is also disclosed in Japanese Patent Laid-Open No. 9-74607. Moreover, one example of a hydraulic control apparatus for an automatic transmission is disclosed in Japanese Patent Laid-Open No. 7-71586.
According to the invention disclosed in the above-mentioned Laid-Open No.2002-225578, however, there is no description about how to control the speed change mechanism in case of function decline occurs in the actuator for changing the speed change mechanism to the low-state or the high-state. Accordingly, there is room for improvement with respect to this point.